1. Field of the Invention
The present invention relates to a double clutch system for a hybrid electric vehicle. More particularly, the present invention relates to a double clutch system for a hybrid electric vehicle that can prevent starting impact by applying a double clutch system of normal close type and can improve durability by minimizing abrasion of a clutch disk.
2. Description of Related Art
Environmentally-friendly technique of vehicles is very important technique on which survival of future motor industry is dependent. Vehicle makers are focusing on development of environmentally-friendly vehicles so as to meet environment and fuel consumption regulations.
Some examples of future vehicle technique are an electric vehicle (EV) and a hybrid electric vehicle (HEV) that use electrical energy, and double clutch transmission (DCT) that improves efficiency and convenience.
In addition, the vehicle makers promote improvement of efficiency in a power delivery system so as to meet exhaust regulation of countries and improve fuel consumption performance. In order to improve efficiency of the power delivery system, the vehicle makers are trying to put an idle stop and go (ISG) system and a regenerative braking system to practical use.
Meanwhile, the hybrid electric vehicle is a vehicle using more than two power sources, and more than two power sources are combined in various ways. Typically, the hybrid electric vehicle uses a gasoline engine or a diesel engine driven by fossil fuel and a motor/generator driven by electrical energy.
In addition, one example of a transmission applied to the hybrid electric vehicle is the DCT. According to the DCT, two clutches are applied to a manual transmission layout. Therefore, efficiency and convenience may be improved.
That is, the DCT achieves odd-numbered-speeds and even-numbered-speeds alternately by using two clutches. A mechanism achieving the odd-numbered-speeds and the even-numbered-speeds alternately improves shift feel so as to solve problems of a conventional manual transmission (MT) and an automated manual transmission (AMT).
However, since both two clutches are clutches of normal open type in a conventional double clutch transmission of a vehicle, at least one clutch should be operated at starting. Therefore, starting impact may occur. In addition, shifting time should be short due to thermal capacity of the clutches at shifting. Therefore, shift shock is great compared with an automatic transmission.
In order to minimize the starting impact, the clutches are led to slip. However, abrasion of clutch disks and energy loss may be great and the vehicle may slide downward due to clutch slip at starting on an uphill road.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.